CEPHALOPODA. 
283 
toward the outer chamber, varying from three to five mm. in the length of 
ninety mm. 
Septa and siphuncle not observed. Sutures curving and oblique, but 
slightly impressed on the internal mould. Ventral side indicated by a longi¬ 
tudinal carina along the cast of the chamber walls. 
The test has a thickness of nearly one mm. Its surface-markings are 
unknown. 
The specimen figured has a length of 190 mm., and embraces more than 
thirty of the air-chambers, with a portion of the chamber of habitation, 
which has a diameter of thirty mm. near the aperture. 
This species is associated with 0. Marcellense in the Goniatite limestone of 
the Marcellus shale, and is distinguished by its more frequent septa, the curved 
and oblique sutures, and more gradually enlarging tube. 
Formation and locality. From the Goniatite limestone of the Marcellus shale 
at Manlius, N. Y. 
Orthoceras subulatum. 
PLATES XXXVIII, FIG. 3 ; LXXXIV, FIGS. 1, 2, 4, 6-10; LXXXVI, FIGS. 1, 2. 
Slender Orthocera, Vanuxem. Geolog'. Survey of N. Y.: Rep. Third Dist., p. 148. 1842. 
Orthoceras subulatum, Hall. Geolog-. Surv. of N. Y. : Rep. Fourth Dist., p. 180, fig. 1. 1843. 
“ “ “ Descriptions of New Species of Fossils, etc., p. 49. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 77. 1862. 
“ “ “ Illustrations of Devonian Fossils: Cephalopoda. Explanation of pi. 38. 1876. 
Shell straight, regularly enlarging from the apex to near the aperture. Trans¬ 
verse section circular. Apical angle varying, in normal and compressed 
specimens, from six to nearly eight degrees. Initial extremity observed, 
but the characters are obscure. 
Chamber of habitation well developed, having a length equal to about 
three times its diameter at the last septum, regularly expanding to a point 
near the aperture ivhere it is slightly contracted. Air-chambers numerous, 
increasing in depth from the apex to the outer chamber, where the depth is 
about three mm. 
